An optical fiber is a glass fiber that carries light along its length. Optical fibers are widely used in fiber-optic communications, which permits transmission over longer distances and at higher bandwidths (data rates) than other forms of communications. Fibers are used instead of metal wires because signals travel along them with less loss, and they are also immune to electromagnetic interference.
Light is kept in the core of the optical fiber by total internal reflection. This causes the fiber to act as a waveguide. Fibers which support many propagation paths or transverse modes are called multi-mode fibers (MMF), while those which can only support a single mode are called single-mode fibers (SMF). MMF generally have a larger core diameter, and are used for short-distance communication links and for applications where high power must be transmitted. SMF are used for most communication links longer than 550 meters (1,800 ft).
Throughout this patent application, attenuation in fiber optics, also known as transmission loss, is defined as the reduction in intensity of the light beam (or signal) with respect to distance traveled through a transmission medium. Attenuation loss coefficients in optical fibers usually are reported using units of decibels per kilometer, abbreviated dB/km.
Attenuation is an important factor limiting the transmission of a digital signal across large distances. Thus, much research has gone into both limiting the attenuation and maximizing the amplification of the optical signal. Empirical research has shown that attenuation in optical fiber is caused primarily by both scattering and absorption.
In 1965, Charles K. Kao {one of three winners of the 2009 Nobel Prize in physics for “groundbreaking achievements concerning the transmission of light in fibers for optical communication”} and George A. Hockham of the British company Standard Telephones and Cables (STC) were the first to promote the idea that the attenuation in optical fibers could be reduced below 20 decibels per kilometer (dB/km), allowing optical fibers to be a practical medium for communication. They proposed that the attenuation in fibers available at the time was caused by impurities, which could be removed, rather than fundamental physical effects such as scattering. The crucial attenuation level of 20 dB/km was first achieved in 1970, by researchers Robert D. Maurer, Donald Keck, Peter C. Schultz, and Frank Zimar working for American glass maker Corning Glass Works, now Corning Incorporated. They demonstrated a fiber with 17 dB/km attenuation by doping silica glass with titanium. A few years later they produced a fiber with only 4 dB/km attenuation using germanium dioxide as the core dopant. The achievement of such low attenuations ushered in optical fiber telecommunications and enabled the internet.
The following U.S. Patent is incorporated by reference in its entirety: U.S. Pat. No. 6,014,488 issued on Jan. 11, 2000.
Microbends are sharp but microscopic curvatures in an optical fiber involving local axial displacements of a few micrometers and spatial wavelengths of a few millimeters. Microbends can be induced by thermal stresses and/or mechanical lateral forces. When present, microbends attenuate the signal transmission capability of the coated optical fiber. Thus for the success of a telecommunications network it is known each telecommunications system has a limit to the amount of tolerable increase in attenuation for optical fiber and that to avoid reaching that limit it is well to reduce microbending overall because reducing microbending, reduces the increase in attenuation.
One of the critical driving forces for the development of optical fiber coating technology is increased user demands on videos. For the existing technology of optical fiber coating, 2G network application is sufficient. However, the future networks, such as 3G, 4G, and IPTV, high definition television (HDTV), video conferencing and other high bandwidth applications will impose a higher requirement for the performance of optical fiber, therefore the requirement of performance of the optical fiber coating will become higher and higher.
In order to meet the huge demand of video applications on the internet, the telecommunication network of next generation requires the support of transmission of greater capacity, longer distance and broader spectral range, and the performance of the current generation of optical fibers G652 was developed for long haul straight alignment utility; therefore G562 is not suitable to meet the requirements of Fiber to the Home (FTTH) challenges.
As optical transport of communication signals migrates into homes and MDU's (Multiple Dwelling Units), optical glass fibers are encountering tighter bends, requiring optical fiber producers to offer G657 Macrobend resistant fibers. At the same time, increasing demands for bandwidth are putting strains on the available margin in deployed networks.
The first generation of radiation curable DeSolite Radiation curable Supercoatings™ (trademark of DSM IP Assets B.V.) for optical fiber are described and claimed in these U.S. Patent Applications, which are hereby incorporated by reference in their entirety: U.S. patent application Ser. No. 11/955,935, filed Dec. 13, 2007, published as US 20080226916 on Sep. 19, 2008; U.S. patent application Ser. No. 11/955,838, filed Dec. 13, 2007, published as US 20080241535 on Oct. 23, 2008; U.S. patent application Ser. No. 11/955,547, filed Dec. 13, 2007, published as US 20080226912 on Sep. 19, 2008; U.S. patent application Ser. No. 11/955,614, filed Dec. 13, 2007, published as US 20080226914 on Sep. 19, 2008; U.S. patent application Ser. No. 11/955,604, filed Dec. 13, 2007, published as US 20080226913 on Sep. 19, 2008;
U.S. patent application Ser. No. 11/955,721, filed Dec. 13, 2007, published as US 20080233397 on Sep. 25, 2008; U.S. patent application Ser. No. 11/955,525, filed Dec. 13, 2007, published as US 20080226911 on Sep. 19, 2008; U.S. patent application Ser. No. 11/955,628, filed Dec. 13, 2007, published as US 20080226915 on Sep. 19, 2008; and U.S. patent application Ser. No. 11/955,541, filed Dec. 13, 2007, published as US 20080226909 on Sep. 19, 2008.
U.S. patent application Ser. No. 11/955,541, filed Dec. 13, 2007, published on Sep. 18, 2009 as US Published Patent Application 20080226909, entitled “D1381 RADIATION CURABLE SUPERCOATINGS FOR OPTICAL FIBER” describes and claims Radiation Curable Supercoatings for Optical Fiber as follows:
Supercoatings suitable for coating an optical fiber;
wherein the Supercoatings comprise at least two layers, wherein the first layer is a Primary Coating that is in contact with the outer surface of the optical fiber and the second layer is a Secondary Coating in contact with the outer surface of the Primary Coating,
wherein the cured Primary Coating on the optical fiber has the following properties after initial cure and after one month aging at 85° C. and 85% relative humidity:                A) a % RAU of from about 84% to about 99%;        B) an in-situ modulus of between about 0.15 MPa and about 0.60 MPa; and        C) a Tube Tg, of from about −25° C. to about −55° C.;        
wherein the cured Secondary Coating on the optical fiber has the following properties after initial cure and after one month aging at 85° C. and 85% relative humidity:                A) a % RAU of from about 80% to about 98%;        B) an in-situ modulus of between about 0.60 GPa and about 1.90 GPa; and        C) a Tube Tg, of from about 50° C. to about 80° C.        
With the recent launch of the DeSolite Supercoatings™ line of Radiation curable Supercoatings for optical fiber, by DSM Desotech, see www.Supercoatings.com it has been reported that use of Supercoatings has great positive effect upon the microbending characteristics of the optical fiber. Thus using Supercoatings is known to reduce the amount of microbending in an optical fiber and reducing the amount of microbending reduces the amount of attenuation in the telecommunications network
As the demand for ever increasing bandwidth develops in the internet and current telecommunications devices, the demand for optical fiber that is attenuation resistant will also increase. Thus the demand for radiation curable Supercoatings will increase. As the demand for attenuation resistant optical fiber and radiation curable Supercoatings increases it would be desirable to have a method for selecting and formulating radiation curable Supercoatings for optical fiber.